The present invention relates to a filter device and filtration process and more particularly to a two-stage batch filter apparatus and process for removing liquid from liquid-solid mixtures.
Both municipal and industrial waste water treatment systems are faced with ever-increasing demands for improved quality of the effluent they generate. Recent clean water legislation mandates that all municipal and industrial waste water treatment systems must meet far more demanding standards in terms of suspended and dissolved solids, heavy metal content and the like, than has heretofore been the case. The waste water engineering industry is now searching to find practical systems which efficiently treat widely varied input loads and which can be operated simply at a reasonable cost. It is also a great advantage to any such waste water treatment system if the "solid" waste product which is produced has some further utility, and if the filtrate is clear not only of suspended but of dissolved solids.
The most significant problem in extracting suspended solids in a waste water treatment system is extracting the highest percentage of solids from the composition being fed into the system. The percentage of solids which can be extracted will vary, given the percentage of solids in the input load, the composition of the input fed into the system, the percentage of organic versus inorganic matter, the weight of the suspended matter, and various other factors. In general, most waste water dewatering systems obtain a solids level of between 15% and 30%, with the latter being achieved only in long throughput processes at considerable cost. The various dewatering systems in use (screws, honeycomb rolls, drum presses, etc.) all have significant limitations.
U.S. Pat. No. 3,687,287 to Gwilliam (Gwilliam I) discloses a two-stage method of reducing the liquid content of a slurry which utilizes a pressure filter comprising a cylindrical filter element, inner and outer tubular bodies, and an impermeable elastic sleeve which divides the filter into two compartments, a filtration compartment and a pressure compartment. The slurry is forced through a filter element under low pressure to remove most of the liquid to form a filter cake, then the elastic sleeve is deformed under high pressure to squeeze additional liquid out of the cake. The disclosed process uses high pres sure (500 psi) which can create safety problems and which is also expensive to generate. In addition, this process and apparatus uses blasts of compressed air to remove the filter cake from the filter element. This requires the additional process steps of lowering the entire inner tubular body, introducing compressed air blasts until the cake is discharged, and then raising the inner tubular body back into its original position.
U.S. Pat. No. 3,753,499 to Gwilliam (Gwilliam II) discloses a two-stage pressure filter for reducing the liquid content of a slurry, like Gwilliam I, that comprises a cylindrical filter element, inner and outer tubular bodies, and an impermeable elastic sleeve dividing the filter into two compartments. The elastic sleeve in Gwilliam II has at least one annular portion which is substantially thicker than the remainder thereof to yield a thinner filter cake at the position corresponding to the thicker elastic sleeve portion. The object is to produce a filter cake that is thinner at some portions in an attempt to facilitate discharge of the cake. However, as in Gwilliam I, it is still necessary to utilize the additional steps of lowering the entire inner tubular body, introducing the compressed air blasts until the cake is discharged, then raising the inner tubular body back into its original position.
U.S. Pat. No. 4,533,472 to Verri et al. discloses a two-stage pressure filter comprising a tubular filter fabric supported by a perforated basket and a tubular membrane which divides the filter into an annular filtration space and an annular pressure space. A first stage forces a liquid slurry through a filter fabric to form a filter cake and a second stage introduces air pressure to deform the membrane thus squeezing additional liquid from the filter layer. The filter cake is discharged by the operation of a hydraulic actuator and shaft which removes the basket and membrane arrangement from its original position. This turns the filter fabric inside-out to discharge the filter cake. Verri et al. thus also includes an additional mechanical step requiring the use of a hydraulic actuator and shaft.
U.S. Pat. No. 3,900,403 to Randle et al. discloses a cylindrical pressure filter similar to Gwilliam and Verri et al., except that the process consists of one stage only--a slurry is forced through a filter element by means of a pressurized impermeable sleeve to remove the liquid and form a "dry" filter cake. The filter cake is discharged either by injecting blasts of air and actuating a cylinder to slide down the filter cloth to force the cake off the cloth, or by vibrating the entire filter body by means of a torsional mode transducer. Either means of removing the filter cake represents additional mechanical steps with associated equipment.
All of these patents disclose batch filters which utilize an impermeable sleeve to squeeze a filter cake formed on a filter cloth. However, all require additional mechanical steps and equipment to achieve the removal of the filter cake. Therefore, there exists a need for a two-stage cylindrical pressure filter apparatus and process which can remove up to 50% of the liquid from a liquid/solid mixture, whereby the filter cake formed is removed simply, effectively, economically and safely without the requirement of costly, maintenance-intensive, mechanized steps.
It is an object of the present invention to provide a two-stage cylindrical pressure filter apparatus and process wherein in the first stage, a slrrry is forced through a filter means under low pressure to form a filter cake, and in the second stage, an elastomeric bladder is deformed under higher pressure into contact with the filter cake to squeeze additional liquid from the cake achieving removal of up to 50% of solids.
It is another object of the present invention to provide such a two-stage batch filter apparatus and process which achieves safe, economical, and effective discharge of the filter cake formed.
It is another object of the present invention to provide a two-stage batch filter apparatus and process which operates at lower pressures in the second stage than similar filters heretofore found in the art.
It is a further object of the present invention to provide a two-stage batch filter apparatus and process for removing liquid from a liquid/solid mixture whereby the solid matter remaining after filtration can be utilized as fuel to provide sufficient energy to operate the filter itself.
It is another object of the present invention to provide a filter apparatus and process whereby the filter cake formed on the filter member provides structural support for the perforated filter support doors.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalitiss and combinations particularly pointed out in the appended claims.